The speed of an asynchronous machine is generally controlled by regulating the electromagnetic torque of the machine.
For this purpose, asynchronous rotary machines are generally provided with a regulator receiving as input a reference value for the electromagnetic torque, together with one or more sampled signals representing the electromagnetic torque of the machine and derived from a measurement of the stator current.
In order to servo-control the electromagnetic torque of the machine on the reference torque value, the regulator proceeds at each sampling instant with a prediction of the value of the torque at the following sampling instant, and it modifies the control voltage accordingly.
One of the main concerns in most industrial applications is to increase the dynamic performance of such regulators, and in particular to increase the dynamic range of the torque.
In order to enable such a system to have a good dynamic range for its torque, it is necessary for the chopper frequency of the inverter to be large compared with the dynamic range that it is desired to obtain, since otherwise compensation is poorly performed and performance suffers. In particular, the efficiency of the inverter and of the motor decrease so the losses to be dumped increase.
One solution to this problem consists in providing the system with low-loss electronic components. However that solution is unacceptable insofar as it contributes to increasing very considerably the cost of the power supply circuit of the machine.